US7282347B2 - Method for extracting quantitative information relating to interactions between cellular components - Google Patents

Method for extracting quantitative information relating to interactions between cellular components Download PDF

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US7282347B2
US7282347B2 US10/332,065 US33206503A US7282347B2 US 7282347 B2 US7282347 B2 US 7282347B2 US 33206503 A US33206503 A US 33206503A US 7282347 B2 US7282347 B2 US 7282347B2
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cells
cell
gfp
rolipram
anchor
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Sara Petersen Bjorn
Ole Thastrup
Bernard Robert Terry
Grith Hagel
Soren Jensby Nielsen
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Fisher BioImage ApS
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
    • G01N33/50—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing
    • G01N33/68—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing involving proteins, peptides or amino acids
    • G01N33/6803—General methods of protein analysis not limited to specific proteins or families of proteins
    • G01N33/6845—Methods of identifying protein-protein interactions in protein mixtures
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
    • G01N33/50—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing
    • G01N33/5005—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing involving human or animal cells
    • G01N33/5008—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing involving human or animal cells for testing or evaluating the effect of chemical or biological compounds, e.g. drugs, cosmetics
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
    • G01N33/50—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing
    • G01N33/5005—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing involving human or animal cells
    • G01N33/5008—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing involving human or animal cells for testing or evaluating the effect of chemical or biological compounds, e.g. drugs, cosmetics
    • G01N33/502—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing involving human or animal cells for testing or evaluating the effect of chemical or biological compounds, e.g. drugs, cosmetics for testing non-proliferative effects
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
    • G01N33/50—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing
    • G01N33/5005—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing involving human or animal cells
    • G01N33/5008—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing involving human or animal cells for testing or evaluating the effect of chemical or biological compounds, e.g. drugs, cosmetics
    • G01N33/502—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing involving human or animal cells for testing or evaluating the effect of chemical or biological compounds, e.g. drugs, cosmetics for testing non-proliferative effects
    • G01N33/5032—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing involving human or animal cells for testing or evaluating the effect of chemical or biological compounds, e.g. drugs, cosmetics for testing non-proliferative effects on intercellular interactions
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
    • G01N33/50—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing
    • G01N33/68—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing involving proteins, peptides or amino acids

Definitions

  • the present invention relates to measurement of interactions between two components wherein the two components are present in a cell, and where both components are most usually wholly or mainly proteinaceous in composition (i.e. the interaction is a protein-protein interaction, or protein-protein binding event).
  • GRIP GRIP assisted Readout of Interacting Proteins
  • the present invention also relates to an extraction buffer used in high throughput screening for drugs that affect the intracellular distribution of intracellular components.
  • the extraction buffer comprises a cellular fixation agent and a cellular permeabilization agent.
  • the second group includes all methods designed to work within living cells. Of these, many have been developed to work in yeast cells (yeast two hybrid, reverse yeast two hybrid and variations thereof) but some have been adapted for use in mammalian cell systems. Cellular methods for detection of protein interactions have been well reviewed by Mendelsohn, A. R., Brent, R. (1999) (Science 284(5422):1948).
  • FRET fluorescence resonance transfer
  • coincidence analysis a variant of fluorescence correlation spectroscopy
  • fluorescence lifetime changes The last three categories are more normally applied under simplified in vitro conditions, but attempts are being made to move them into the more complex environment of the living cell.
  • the first heterologous conjugate comprises the first protein of interest conjugated to a detectable group (e.g. GFP).
  • the second heterologous conjugate comprises a second protein of interest conjugated to a protein that specifically binds to an internal structure within the cell upon stimulation with phorbol ester.
  • binding between the two proteins of interest can be visualised as the detectable group will be located bound to internal structure within the cell.
  • Proteins(-GFP) that are not “anchored” in an intracellular organelle or compartment, but are more or less mobile in the cytosol, will diffuse into the surrounding medium upon cell permeabilization, at a rate largely governed by the degree of permeabilisation imposed. It is difficult to control the release of cellular contents by permeabilization since detergents have the tendency to not only disrupt the membrane but also over time disrupt intracellular components. Beside this, damaging the membrane will start some uncontrolled protease activity with the same unintentional result. This phenomenon is also seen when using non detergent permeabilization (eg. Digitonin). Fixative agents are commonly used to preserve structural integrity in cells during the processes necessary to prepare biological material for microscopy.
  • Fixatives aimed at preserving or stabilising protein structures within cells can be divided into two groups; those that coagulate proteins, such as organic acids or alcohols (e.g. acetic acid, ethanol), and those that cross-link proteins together into an insoluble network, such as the aldehydes (e.g. formaldehyde or glutaraldehyde).
  • the rate of fixation by such agents is governed by their rate of penetrance into cells together with the rate of chemical cross-linking or coagulation that they can achieve.
  • the processes and methods of cellular fixation have been thoroughly studied and described in the scientific literature (see, for example, Fixation for Electron Microscopy by M. A. Hayat, 1981, Academic Press, New York).
  • Translocation usually involves changes in the effective mobility of at least one protein within the cell, either through changes in interaction between that component and an anchored (or effectively non-mobile) component or through a change in location or compartmentation of the component, for example a transfer from the extra-nuclear cytoplasm into the nucleus itself. Changes in interaction or compartmentation constitute translocation. RedistributionTM is the art of making translocation a measurable event (WO98/45704). Translocation may involve change in mobility or compartmentation of a component to which the component of interest is attached, for example a motor protein by which the component of interest is carried. Some translocations involve sub-microscopic distances, for instance the interaction between a soluble signaling protein in the cytoplasm and an adjacent actin filament or intracellular membrane.
  • RedistributionTM is measured by “imaging”, which is very time consuming and inconvenient for drug screening in HT format.
  • RedistributionTM assays often comprise cell lines stably expressing a particular protein of interest, (most often that protein being an engineered protein fusion between the protein of interest and a luminescent protein such as GFP). In such cells, it may be the case that the component of interest is overexpressed to some degree relative to the other components in the cell with which it should interact. This can lead to a masking of the translocation event by excess amounts of the protein of interest that cannot physically interact with the limited number of partner components available in the cell. In such cases, removal of the excess component of interest may be sufficient to unmask the translocation that has occurred.
  • the interaction between Sos and Grb2 can be measured in various ways. As shown in the Example 7, cells co-transfected with a PDE4A4-SosA conjugate and with a Grb2-EGFP conjugate illustrate the binding between SosA and Grb2.
  • the conjugates are PKAcat-hGrb2 and EGFP-Sos-Cterm.
  • the advantage of the PKAcat conjugates is that no special treatment is necessary in order to visualise interaction, as long as levels of cAMP within cells remain sufficiently low so that PKA is predominately attached to it regulatory subunits.
  • the conjugates are Cys1-Grb2 and EGFP-Sos-Cterm.
  • the possible advantage of the Cys1 conjugates are that they will take one component of a pair to the plasma membrane when treated with PMA or some other activation stimulus. This special location may be necessary in order to activate interaction of the components being studied.
  • Example 3 describes a generic way to produce cell lines by co-transfection of two plasmids, each expression a heterologous conjugate.
  • PDE4A4 based anchor probes as anchor-proteins an average of two dense aggregates is formed by treatment with rolipram. These aggregates can by detected directly with an antibody directed against the unique C-terminal peptide sequence of PDE4A. The dense aggregates (the spots) will disappear when either rolipram is removed or competed against with one of a particular class of PDE4 inhibitors (e.g. RP73401). It is important to note that the treatment with rolipram does not affect the levels of cAMP in the cells (Example 14).
  • Example 4 describes that using PKAcata based anchor probes as anchor-proteins aggregates are formed in the cytoplasm when the concentration of cytoplasmic cAMP is low. These aggregates can by detected directly with an antibody directed against PKAc or against the PKA regulatory subunit. These aggregates disperse into the cytoplasm when cAMP concentrations are elevated.
  • Example 5 describes that using PDE4A1 based anchor probes as anchor-proteins, small perinuclear spots are formed in the cytoplasm in otherwise untreated cells. PDE4A1 spots can by detected directly with an antibody directed against the unique C-terminal peptde sequence of PDE4A. These spots disperse into the cytoplasm when rolipram is added to the cells.
  • Example 6 describes that using Cys1 domain based anchor probes as anchor-proteins redistributes to the plasma membrane when activated e.g. by treatment with PMA.
  • the localisation of the Cys1 domain can be confirmed with antibodies directed against the myc or flag antigens (when myc or flag sequences are included in the genetic construct used to transfect the cells).
  • fixative and permeabilisation aims to preserve local concentrations of the anchored, diffusionally restricted or largely immobile form of the protein of interest while allowing freely mobile or unanchored forms to be released from the cell. It is expected that the process of cell permeabilisation, especially by detergents, will in time remove even relatively immobile, anchored or compartmentalised proteins from the cell, and hence a balance must be found between the rate of permeabilisation and solubilisation caused by the detergent agent, and the rate at which cross-linking or fixation takes place. This balance may be achieved by careful selection of the fixative and premeabilisation agents, controlling the relative concentations of these agents, also by controlling the physical and chemical conditions under which the agents work (pH, osmolarity or ionic strength, temperature).
  • Example 10 the change in mobility of BAD caused by the binding between the 14-3-3 protein and BAD is measured using a PDE4A4-14-3-3 and an EGFP-BAD fusion.
  • the PDE4A4-14-3-3 protein is stuck in spots within the cell due to previous treatment with rolipram.
  • Example 11 shows the same principle applied to the RedistributionTM of NFkB(p65) from cytosol to nucleus upon stimulation of NFkB.
  • the optimization of the extraction buffer, to identify the optimal ratio between the cellular fixation agent and the cellular permeabilisation agent is illustrated in Example 12.
  • the redistribution-trap method is different from any of the above-mentioned methods in that it utilises positional information from PDE4 and in one aspect distribution of a GFP-labelled fluorescent probe in a cell, to indicate the presence or absence of an interaction between specific components. That it does so in the complex environment of the cell, which allows for the influence of factors which may modulate an interaction in the same way as would happen in the native system, adds important physiological relevance to the method. Since it is based on non-destructive fluorescence imaging, meaning that the cells can be live and active whilst being monitored, and since it is based on non-disturbing treatment with e.g.
  • the redistribution-trap method also allows transient or conditional interactions to be monitored. Transient or conditional interactions may occur when components are phosphorylated or otherwise modified during their cycle of operation (e.g. transmission of a signal), and such modifications are common amongst components of intracellular signalling pathways. As the method does not rely on covalent interactions nor that the components need have a specific orientation upon interaction, the method is very sensitive and allow for measurement of even low affinity interactions.
  • One aspect thus relates to a method for detecting if a compound modulates an intracellular protein interaction comprising the steps of:
  • the redistribution-trap method makes use of the fact that many signalling components redistribute within the cell to specific locations upon specific stimuli or treatments. If those components can be labelled in some way to make them visible in the cell, their location can be monitored and measured by a number of image-based techniques. Since imaging techniques are non-destructive, they allow measurements to be made on living cells, hence active processes can be followed over time if that is required—as may be the case when transient events need to be monitored. This application details how the knowledge that a particular component will redistribute upon receiving a certain stimulus (the “anchor” stimulus) can be harnessed, to create a system to explore interactions between intracellular components.
  • a component is known to distribute to a known cellular location upon a certain stimulus, another component (the “bait”) may be covalently attached to the first (the “anchor”) and, given the appropriate anchor stimulus, will be expected to assume the same distribution in the cell as the anchor component to which it is attached.
  • a further component (the “prey”), which is expected to interact with the bait component, is introduced into the same cell.
  • the prey component is labelled in some way to make it visible in the cell. If an interaction occurs between bait and prey (perhaps requiring a further interaction “stimulus”), then the prey component also takes up the same distribution within the cell as the anchor-bait component, but only if the appropriate anchor stimulus has also been applied.
  • Anchor systems can be designed to achieve redistribution to compartments or locations within cells where the interacting components may experience the influences that would normally be required to modulate the interaction between those components.
  • some components may normally require to be phosphorylated or dephosphorylated by enzymes sequestered in the plane of the plasma membrane—for such components it would be appropriate for an anchor system to be chosen such that the anchor stimulus redistributed the anchor probe to the plasma membrane, to allow the interacting components to be appropriately modified.
  • An example of such an anchor system would be one based on the Cys1 domain of PKC ⁇ .
  • the method also allows for targeting interactions to different locations within the cell with the purpose of studying whether location specific conditions are necessary for the interaction to occur.
  • one or both interacting components are targeted to the nuclear compartment.
  • one or both interacting components are targeted to mitochondria outer or inner membranes.
  • one or both interacting components are targeted to different regions of Golgi bodies.
  • one or both interacting components are targeted to focal adhesion complexes.
  • one or both interacting components are targeted to cytoskeletal structures such as F-actin strands or microtubular bundles.
  • one or both interacting components are targeted to the plasma membrane.
  • one or both interacting components are targeted to cytoplasmic granules or aggregates such as those formed by PDE4A4 in the presence of rolipram.
  • a specific embodiment of the present invention relates to a method wherein the specific binding to the internal structure within the cell is induced by an anchor stimulus that by itself has little likelihood of stimulating or inhibiting signalling activity within the cell of interest.
  • PDE4A4 Due to the strong anchoring response of PDE4A4 to rolipram and other specific PDE4 inhibitors such as RS25344, PDE4A4 is most preferred as the anchoring species. Furthermore, it seems that the attachment of PDE4A4 to it's anchor site is not affected by he presence of additional parts attached to the C-terminal of the PDE4A4 molecule, here these attachments can be of very variable size (from less than 10 kDa to at least 150 kDa). Thus, a specific embodiment of the present invention relates to a method as described above wherein the specific binding is induced by addition of the anchor stimulus rolipram and wherein the anchor protein is PDE4A4.
  • the particular utility of stimulus-induced distributions is that in one and the same cell it is possible to switch on a distinctive distribution where previously there was none.
  • This not only guarantees, in advance, that the distinctive distribution is purely a result of specific interaction between anchored and detectable components (the anchor component responding to the stimulus is “invisible” unless decorated by the detectable component), but also guarantees that this interaction will give a signal that is measurable by the assay equipment configured to detect the specific and expected distribution of the anchor component. In effect this latter point means that many different interactions can be measured and assayed without the need to reconfigure the measuring equipment or the assay method.
  • the inducing stimulus provides a reference compound in screening assays by which the maximum and minimum expected signals for an assay can be determined.
  • a component is known to have an inherently distinctive cellular distribution
  • another component may be covalently attached to the first (the “anchor”) and, without any anchor stimulus, will be expected to assume the same distribution in the cell as the anchor component to which it is attached.
  • a further component (the “prey”), which is expected to interact with the bait component, is introduced into the same cell.
  • the prey component is labelled in some way to make it visible in the cell. If an interaction occurs between bait and prey (perhaps requiring a further “interaction stimulus”), then the prey component also takes up the same distribution within the cell as the anchor-bait component, even without application of an anchor stimulus due to the specific location in the first place.
  • Anchor systems can be designed to achieve redistribution to compartments or locations within cells where the interacting components may experience the influences that would normally be required to modulate the interaction between those components.
  • the spot like cytoplasmic distribution of PKA can be dissolved by addition of forskolin; the spot like cytoplasmic distribution of PDE4A1 can be dissolved by addition of rolipram; the spot like nuclear distribution of histonedeacetylase 5 (HDAC5) is dissolved by Trichostatin A (TSA); or the specific binding of the anchor protein is PLC-delta to the cell membrane is dissolved by addition of ATP and distributed within the cytoplasm.
  • HDAC5 histonedeacetylase 5
  • TSA Trichostatin A
  • the stimulus provides a means to check whether that distinct distribution is the result of interaction between anchored and detectable components, or results from some inherent tendency of the detectable component to assume that distinct distribution within the cell. The check for this can be made in one and the same cell that the assay for interaction is measured.
  • the anchor stimulus such as those based on PDE4A1, PKAcat, PLCdelta or HDAC5
  • the stimulus provides a means to check whether that distinct distribution is the result of interaction between anchored and detectable components, or results from some inherent tendency of the detectable component to assume that distinct distribution within the cell. The check for this can be made in one and the same cell that the assay for interaction is measured.
  • systems with an initial distinct distribution of the anchor component share the advantages of being able to assay many different interactions with one configuration of equipment and assay protocol.
  • the anchor stimulus in each case again provides a reference compound in screening assays by which the maximum and minimum expected signals for an assay can be determined.
  • the particular additional advantage of those systems where the anchor stimulus disperses a distribution is that no pretreatment or co-treatment of cells with distribution stimuli is necessary during the assay procedure, precluding any possibility that the anchor stimulus may interfere, directly or indirectly, with the interaction that is being tested.
  • the term “compound” is intended to indicate any sample, which has a biological function or exerts a biological effect in a cellular system.
  • the sample may be a sample of a biological material such as a sample of a body fluid including blood, plasma, saliva, milk, urine, or a microbial or plant extract, an environmental sample containing pollutants including heavy metals or toxins, or it may be a sample containing a compound or mixture of compounds prepared by organic synthesis or genetic techniques.
  • the compound may be small organic compounds or biopolymers, including proteins and peptides.
  • the compound to be tested can be regarded as a special interaction stimulus.
  • Xenopus oocytes or insect cells such as the sf9 cell line, or mammalian cells isolated directly from tissues or organs taken from healthy or diseased animals (primary cells), or transformed mammalian cells capable of indefinite replication under cell culture conditions (cell lines).
  • primary cells healthy or diseased animals
  • transformed mammalian cells capable of indefinite replication under cell culture conditions cell lines.
  • the cells used are mammalian cells. This is due to the complex biochemical interactions specific for each cell type.
  • mammalian cell is intended to indicate any living cell of mammalian origin.
  • the cell may be an established cell line, many of which are available from The American Type Culture Collection (ATCC, Virginia, U.S.A.) or similar Cell Culture Collections.
  • the cell may be a primary cell with a limited life span derived from a mammalian tissue, including tissues derived from a transgenic animal, or a newly established immortal cell line derived from a mammalian tissue including transgenic tissues, or a hybrid cell or cell line derived by fusing different cell types of mammalian origin e.g. hybridoma cell lines.
  • the cells may optionally express one or more non-native gene products, e.g. receptors, enzymes, enzyme substrates, prior to or in addition to the fluorescent probe.
  • Preferred cell lines include but are not limited to those of fibroblast origin, e.g. BHK, CHO, BALB, NIH-3T3 or of endothelial origin, e.g.
  • HUVEC HUVEC
  • BAE bovine artery endothelial
  • CPAE cow pulmonary artery endothelial
  • HLMVEC human lung microvascular endothelial cells
  • airway epithelial origin e.g. BEAS-2B
  • pancreatic origin e.g. RIN, INS-1, MIN6, bTC3, aTC6, bTC6, HIT
  • hematopoietic origin e.g.
  • adipocyte origin e.g. 3T3-L1
  • human pre-adipocytes or of neuroendocrine origin, e.g. AtT20, PC12, GH3, muscle origin, e.g. SKMC, A10, C2C12, renal origin, e.g. HEK 293, LLC-PK1, or of neuronal origin, e.g. SK-N-DZ, SK-N-BE(2), HCN-1A, NT2/D1.
  • the examples of the present invention are based on CHO cells. Therefore fibroblast derived cell lines such as BALB, NIH-3T3 and BHK cells are preferred.
  • the two heterologous conjugates are introduced into the cell as plasmids, e.g. two individual plasmids mixed upon application to cells with a suitable transfection agent such as Fugene (see Example 3, Example 4, Example 5 and Example 6) so that transfected cells express and integrate both the first and the second heterologous conjugates simultaneously.
  • a suitable transfection agent such as Fugene (see Example 3, Example 4, Example 5 and Example 6)
  • Fugene see Example 3, Example 4, Example 5 and Example 6
  • Many other means for introduction of one or both of the conjugates are evenly feasible e.g. electroporation, calcium phosphate precipitate, microinjection, adenovirus and retroviral methods, bicistronic plasmids encoding both conjugates etc.
  • protein should have the general meaning. That includes not only the translated product, but also chemically synthesised proteins.
  • proteins translated within the cell the naturally, or induced, post-translational modifications such as glycosylation and lipidabon are expected to occur and those products are still considered proteins.
  • intracellular protein interaction has the general meaning of an interaction between two proteins, as described above, within the same cell.
  • the interaction is due to non-covalent forces between the protein components, most usually between one or more regions or domains on each protein whose physico-chemical properties allow for a more or less specific recognition and subsequent interaction between the two protein, components involved.
  • the intracellular interaction is a protein-protein binding.
  • the luminophore allows the spatial distribution of the component to be visualised and/or recorded by emitting light.
  • the luminophore is capable of being redistributed in substantially the same manner as the component.
  • the luminophore is capable of being quenched upon spatial association with a component which is redistributed by modulation of the pathway, the quenching being measured as a change in the intensity or lifetime of the luminescence.
  • the luminophore is a fluorophore.
  • the luminophore is a polypeptide encoded by and expressed from a nucleotide sequence harboured in the cell or cells.
  • the luminophore is a part of a hybrid polypepbde comprising a fusion of at least a portion of each of two polypeptides one of which comprises a luminescent polypeptide and the other one of which comprises the component.
  • GFP is especially preferred.
  • green fluorescent protein is intended to indicate a protein which, when expressed by a cell, emits fluorescence upon exposure to light of the correct excitation wavelength (e.g. as described by Chalfie, M. et al. (1994) Science 263, 802-805).
  • a fluorescent protein in which one or more amino acids have been substituted, inserted or deleted is also termed “GFP”.
  • GFP as used herein includes wild-type GFP derived from the jelly fish Aequorea victoria , or from other members of the Coelenterata, such as the red fluorescent protein from Discosoma sp. (Matz, M. V. et al.
  • GFP variants are F64L-GFP, F64L-Y66H-GFP F64L-S65T-GFP, F64L-E222G-GFP.
  • GFP GFP
  • DNA encoding EGFP which is a F64L-S65T variant with codons optimized for expression in mammalian cells is available from Clontech, Palo Alto, plasmids containing the EGFP DNA sequence, cf. GenBank Acc. Nos. U55762, U55763).
  • Another especially preferred variant of GFP is F64L-E222G-GFP.
  • the detectable group preferably is a green fluorescent protein (GFP).
  • the GFP is preferably selected from the group consisting of GFPs having the F64L mutation as defined herein such as F64L-GFP, F64L-Y66H-GFP, F64L-S65T-GFP, EGFP, and F64L-E222G-GFP.
  • the GFP is N- or C-terminally tagged, optionally via a peptide linker, to the biologically active polypeptide or a part or a subunit thereof.
  • the detectable groups is labelled with chemical fluorophores either in situ or by microinjection or otherwise introduced into cells.
  • the detectable group comprises an epitope for antibodies, which are themselves detectable by other methods, either because they are tagged with a fluorophore, or may be detected by a biotin-streptavidin labelling method, or by secondary antibodies labelled with fluorophores etc.
  • epitopes detectable tag such as the myc or flag antigens, which may then be detected with antibodies, which are themselves detectable by other methods, either because they are tagged with a fluorophore, or may be detected by a biotin-streptavidin labelling method, or by secondary antibodies labelled with fluorophores etc.
  • Internal structure refers to a separate, discreet, identifiable component contained within a cell.
  • Such internal structures are, in general, anatomical structures of the cell in which they are contained. Examples of internal structures include both structures located in the cytosol or cytoplasm outside of the nucleus (also called cytoplasmic structures) and structures located within the nucleus (nuclear structures). The nucleus itself including the nuclear membrane is an internal structure.
  • the recording of the detectable group will vary with the detectable group chosen.
  • the emitted light can be measured with various apparatus known to the person skilled in the art.
  • a light source a light source
  • a method for selecting the wavelength(s) of light from the source which will excite the luminescence of the luminophore a device which can rapidly block or pass the excitation light into the rest of the system
  • a series of optical elements for conveying the excitation light to the specimen, collecting the emitted fluorescence in a spatially resolved fashion, and forming an image from this fluorescence emission (or another type of intensity map relevant to the method of detection and measurement)
  • a bench or stand which holds the container of the cells being measured in a predetermined geometry with respect to the series of optical elements
  • a detector to record the light intensity, preferably in the form of an image
  • the apparatus system is automated.
  • the components in d and e mentioned above comprise a fluorescence microscope.
  • the component in f mentioned above is a CCD camera.
  • the component in f mentioned above is an array of photomultiplier tubes/devices.
  • the actual fluorescence measurements are made in a standard type of fluorometer for plates of microtiter type (fluorescence plate reader).
  • the optical scanning system is used to illuminate the bottom of a plate of microtiter type so that a time-resolved recording of changes in luminescence or fluorescence can be made from all spatial limitations simultaneously.
  • the image is formed and recorded by an optical scanning system.
  • the actual luminescence or fluorescence measurements are made in a FLIPRTM instrument, commercially available from Molecular Devices, Inc.
  • the quantitative information which is indicative of the degree of the cellular response to the influence or the result of the influence on the intracellular pathway is extracted from the recording or recordings according to a predetermined calibration based on responses or results, recorded in the same manner, to known degrees of a relevant specific influence.
  • the degree of redistribution caused by an influence is expressed as the dose of a relevant specific influence causing same degree of cellular response.
  • the present invention can among other things be useful to:
  • one aspect of the present invention relates to a method for measuring a change in mobility of a cellular component caused by an influence, the method comprising:
  • One major advantage of the present invention is that changes in mobility can be measured as a change in light intensity. As will be illustrated below, and as described in the examples, this technique allows RedistributionTM to be detected as a fluorescence intensity change.
  • the instrument for measuring the light emitted from the luminophore is a FLIPR (Molecular Devices).
  • the light emitted from the luminophore is measured on a plate reader.
  • This technique has improved RedistributionTM assays like the NFkB assay (Example 11) and TRAP assays like PDE4A4-trap (Example 10 and Example 12) from a screen time of 4 hrs per plate (imaging) to app. 30 sec. per plate (that is 480 times faster).
  • the change in mobility is characterized in that the component is substantially immobile either prior to contact or incubation with the influence or after contact or incubation with the influence.
  • substantially immobile is defined as the component will not move outside of the detection field during the extraction procedure.
  • the detection field when the cells are washed after extraction, will In essence be the cells (or whatever is left of the cells when permeabilized and chemically fixed).
  • the change in mobility of the component is caused by the component being associated with or adhered to a cellular compartment.
  • the majority of PKAcat-GFP in the inactive form aggregates as spots in the cytoplasm.
  • the PKAcat spots dissolve into the cytosol where the individual PKAcat molecules are much more mobile.
  • the immobility is caused by binding of the component to a binding partner with unknown intracellular distribution.
  • the binding partner is fused to a protein with known substantially immobile intracellular distribution and the component is still coupled to the luminophore.
  • binding between the component and the binding partner will cause the component to be substantially immobile.
  • the change in mobility is a change from a soluble cytoplasmic state to an attached cytoplasmic state. That is, attached to organelles, e.g. attached to IR.
  • the change in mobility is a change from an attached cytoplasmic state to a soluble cytoplasmic state.
  • the change in mobility is a change from a soluble cytoplasmic state to a state wherein the component is attached to the cellular membrane.
  • the change in mobility is a change from a state wherein the component is attached to the cellular memebrane to a state wherein the component is soluble in the cytoplasm.
  • the change in mobility is a change from a soluble cytoplasmic state to a state wherein the component is attached to, or incorporated in, the nucleus. In another aspect the change in mobility is a change from a state wherein the component is attached to, or incorporated in, the nucleus to a soluble cytoplasmic state.
  • the change in mobility is a change from an attached cytoplasmic state to a state wherein the component is attached to, or incorporated in, the nucleus. In another aspect the change in mobility is a change from a state wherein the component is attached to, or incorporated in, the nucleus to an attached cytoplasmic state.
  • Attachment in the cell is anticipated to be mediated by an internal structure e.g. organelle, membrane, cytoskeleton, or a molecular structure.
  • an internal structure e.g. organelle, membrane, cytoskeleton, or a molecular structure.
  • the cellular component is taking part in an intracellular signalling pathway, such as enzymes involved in the intracellular phosphorylation and dephosphorylation processes including kinases, protein kinases and phosphatases, but also proteins making up the cytoskeleton play important roles in intracellular signal transduction.
  • the cellular component is a protein kinase, a protein phosphatase, or a transcription factor.
  • the influence is contact between the mechanically intact living cell or the group of mechanically intact living cells with a chemical substance and/or incubation of the mechanically intact living cell or the group of mechanically intact living cells with a chemical substance.
  • the invention is used as a basis for a screening program, where the effect of unknown influences such as a compound library, can be compared to influence of known reference compounds under standardised conditions.
  • the extraction buffer comprises a cellular fixation agent and a cellular permeabilisation agent.
  • the cellular fixation agent is one, or a mixture of, protein coagulants or protein cross-linking agents, such as ethanol, acetic acid, acrolein, formaldehyde, glutaraldehyde, potassium permanganate, tannic acid, paraformaldehyde. Most preferred fixation agent is formalin.
  • the cellular permeabilisation agent is a, or a mixture of, agents capable of perforating the plasma membrane of the cell such as Streptolysin O, or a anionic, non-ionic, zwitterionic or cationic detergent or detergent buffer such as lauryl sulphate, deoxycholic acid, digitonin, pluronic F68, Saponin, Triton X-100, Triton X-114, nonidet P40, CHAPS, hexadecyltrimethylammonium bromide or an agent inducing osmotic shock like salt or digitoxin.
  • the most preferred permeabilisation agent is Triton X-100.
  • the final wash buffer should be carefully buffered at a pH suitable for obtaining maximal fluorescence from GFP, e.g. between pH 7.5 and 9.0, most preferably at pH 8.5.
  • the buffering capacity should be sufficient to counteract the effects of trace amounts of formalin and Hoechst stain that may remain in or around cells after washing.
  • the ratio between the fixation agent and the permeabilisation agent is of essential importance. On the one side, the cell must be permeabilised to let the mobile component diffuse of out the cell; on the other side, the cell must be chemically fixed to prevent all cellular compartment to diffuse. As illustrated in Examples 10 to 12, it is of highest importance to optimized the ratio in each case since the optimal ratio depends on the cell type and, more importantly, the component and the kind of immobility (as discussed previously).
  • An extraction buffer comprising 0.1% Formaldehyde and 0.1% Triton-X turns out to be a good starting point as that will, in our hands, always improve the assay even though these concentrations might not be optimal.
  • the reference compound is a compound known to cause high degree of change in mobility of the component.
  • PS462 contains a fusion of PDE4A4 and EGFP under the control of a CMV promoter and has resistance to G418 as selectable marker.
  • PDE4A4-EGFP fusion the ca. 1.9 kb C-terminal part of HSPDE4A4 (GenBank Acc. no. L20965), which is common to all PDE4A isoforms, is amplified using PCR with primers 4A-Ct-top and 4A-bottom described below.
  • the sequence of the top primer contains a silent mutation, which introduces a Dra1 site exactly at the beginning of the shared 4A region.
  • the bottom primer includes the common C-terminal sequence minus the stop codon, a BamH1 cloning site, and two extra nucleotides to preserve the reading frame when cloned into pEGFP-N1.
  • the unique ca. 0.8 kb N-terminal part of HSPDE4A4 is amplified using PCR in the presence of 5% DMSO with primers 4A4-top and 4A4N-bottom described below.
  • the top primer includes specific HSPDE4A4 sequences following the ATG, a Kozak sequence, and a Hind3 cloning site.
  • the bottom primer spans the junction of the unique 4A4 N-terminal part and the common 4A C-terminal part, and it contains a silent mutation that introduces a Dra1 site exactly at the beginning of the shared 4A region.
  • the PCR products are digested with the relevant restriction enzymes (Hind3 and Dra1 for the unique N-terminal part and Dra1 and BamH1 for the common C-terminal part), and ligated together into pEGFP-N1 (Clontech, Palo Alto; GenBank Accession number U55762) digested with Hind3 and BamH1. This produces a PDE4A4-EGFP fusion under the control of a CMV promoter.
  • the resulting plasmid is referred to as PS462 (deposited under the Budapest Treaty with Deutsche Sammiung von Mikroorganismen und Zellkulturen GmbH (DSMZ) on Apr. 17, 2000 with DSM 13450).
  • Plasmid PS642 contains a fusion of PDE4A4 and SOS1 under the control of a CMV promoter, and has resistance to zeocin as selectable marker.
  • PS642 is derived from PS614, which is derived from PS462.
  • PS462 is constructed as described above.
  • the neomycin resistance marker on PS462 is replaced with a zeocin resistance marker by digesting PS462 with Avr2, which excises neomycin, and ligating the vector fragment with a ca 0.5 kb Avr2 fragment encoding zeocin resistance. This fragment is isolated by PCR using primers 9655 and 9658 described below with pZeoSV (Invitrogen) as template.
  • Both primers contain Avr2 cloning sites, and flank the zeocin resistance gene including its E. coli promoter.
  • the top primer 9658 spans the Ase1 site at the beginning of zeocin, which can be used to determine the orientation of the Avr2 insert relative to the SV40 promoter which drives resistance in mammalian cells.
  • the resulting plasmis is referred to as PS614.
  • the coding sequence of human SOS1 (GenBank accession number NM — 005633) is isolated from e.g. a human fetus or brain cDNA library by PCR with primers 0099 and 0100 described below.
  • the top primer includes specific SOS1 sequences following the ATG and a BamH1 cloning site.
  • the bottom primer includes specific SOS1 sequence including the stop codon and a Not1 cloning site.
  • the PCR product is digested with restriction enzymes BamH1 and Not1, and ligated into PS614 vector DNA digested with BamH1 and Not1. This creates a fusion between PDE4A4 and SOS1 under the control of a CMV promoter.
  • the resulting plasmid is referred to as PS642.
  • Plasmid PS587 contains a fusion of GRB2 and EGFP under the control of a CMV promoter, and has neomycin resistance as selectable marker.
  • the coding sequence of human GRB2 (GenBank accession number NM — 002086) is isolated from e.g. a human fetus or brain or placenta cDNA library by PCR with primers 0073 and 0074 described below.
  • the top primer includes specific GRB2 sequences following the ATG and a Hind3 cloning site.
  • the bottom primer includes specific GRB2 sequence including the stop codon and an EcoR1 cloning site.
  • the PCR product is digested with restriction enzymes Hind3 and EcoR1, and ligated into pEGFP-N1 vector DNA (Clontech, Palo Alto, GenBank Accession number U55672) digested with Hind3 and EcoR1.
  • the vector may optionally first have been modified to contain a T7 promoter (which can be used for in vitro transcription) immediately upstream of EGFP. This can be achieved by digesting pEGFP-N1 with restriction enzymes Nhe1 and Bgl2, which cut Immediately upstream of EGFP, and ligating the vector fragment with annealed oligos 9949 & 9950.
  • the resulting plasmid is referred to as PS587.
  • Plasmid PS639 contains a fusion of the catalytic subunit of PKA (PKAcat) and GRB2 under the control of a CMV promoter, and has resistance to zeocin as selectable marker.
  • PS639 is derived from PS610, which is derived from PS457.
  • Plasmid PS457 contains a fusion of PKAcat and EGFP under the control of a CMV promoter, and has neomycin resistance as selectable marker.
  • the coding sequence of human PKAcat (GenBank accession number X07767) except the 17 N-terminal amino acids is isolated from e.g. a human liver or spleen cDNA library by PCR with primers 9952 and 9922 described below.
  • the top primer includes specific PKAcat sequences spanning an EcoR1 site near the N-terminus of the coding sequence.
  • the bottom primer includes specific PKAcat sequence minus the stop codon and a BamH1 cloning site.
  • the PCR product is digested with restriction enzymes EcoR1 and BamH1, and ligated into pEGFP-N1 vector DNA (Clontech, Palo Alto, GenBank Accession number U55672) digested with EcoR1 and BamH1.
  • This intermediate is digested with Hind3 and EcoR1 and ligated with annealed oligos 9955 and 9956, which adds remaining N-terminal amino acids to PKAcat, and so creates a fusion between PKAcat and EGFP under the control of a CMV promoter.
  • This construct is referred to as PS457.
  • PS610 is constructed by replacing neomycin resistance on PS457 with zeocin resistance as described above.
  • the coding sequence of human GRB2 is isolated from PS587 described above by PCR with primers 0143 and 0142 described below.
  • the top primer includes specific GRB2 sequences following the ATG and a BamH1 cloning site.
  • the bottom primer includes specific GRB2 sequence including the stop codon and an Xba1 cloning site.
  • the PCR product is digested with restricton enzymes BamH1 and Xba1, and ligated into PS610 vector DNA (isolated from a dam-minus E. coli ) digested with BamH1 and Xba1. This creates a fusion between PKAcat and GRB2 under the control of a CMV promoter.
  • the resulting plasmid is referred to as PS639.
  • Plasmid PS602 contains a fusion of EGFP and the 265 C-terminal amino acids of SOS1 under the control of a CMV promoter, and the neomycin resistance marker.
  • a C-terminal part of the coding sequence of human SOS1 (GenBank accession number NM — 005633) is isolated from e.g. a human fetus or brain cDNA library by PCR with primers 0122 and 0123 described below.
  • the top primer includes specific SOS1 sequences following amino acid number 1067 plus an ATG and an Xho1 cloning site.
  • the bottom primer includes specific SOS1 sequence including the stop codon and a BamH1 cloning site.
  • the PCR product is digested with restriction enzymes Xho1 and BamH1, and ligated into pEGFP-C1 vector DNA (Clontech, Palo Alto, GenBank Accession number U55673) digested with Xho1 and BamH1.
  • pEGFP-C1 vector DNA Clontech, Palo Alto, GenBank Accession number U55673
  • the vector may optionally first have been modified to contain a T7 promoter (which can be used for in vitro transcription) immediately upstream of EGFP as described above.
  • the resulting plasmid is referred to as PS602.
  • Plasmid PS628 contains a fusion of the Cys1 domain of PKCgamma and GRB2 under the control of a CMV promoter, and has resistance to zeocin as selectable marker.
  • PS628 is derived from PS613, which is derived from PS443.
  • Plasmid PS443 contains a fusion of the 90 N-terminal amino acids of human PKCgamma (the Cys1 domain) and EGFP under the control of a CMV promoter, and has neomycin resistance as selectable marker.
  • the Cys1 domain of human PKCgamma (GenBank accession numbers M13977 and Z15114) is isolated from e.g. a human brain cDNA library by PCR with primers 9916 and 9935 described below.
  • the top primer includes specific PKCgamma sequences spanning the ATG and an EcoR1 cloning site.
  • the bottom primer includes specific PKCgamma sequence around amino acid number 90 and an Acc65 cloning site.
  • the PCR product is digested with restriction enzymes EcoR1 and Acc65, and ligated into pEGFP-N1 vector DNA (Clontech, Palo Alto, GenBank Accession number U55672) digested with EcoR1 and Acc65. This creates a fusion between PKCgamma-Cys1 and EGFP under the control of a CMV promoter. This construct is referred to as PS443.
  • PS613 is constructed by replacing neomycin resistance on PS443 with zeocin resistance as described above.
  • the coding sequence of human GRB2 is isolated from PS587 described above by PCR with primers 0143 and 0142 described below.
  • the top primer includes specific GRB2 sequences following the ATG and a BamH1 cloning site.
  • the bottom primer includes specific GRB2 sequence including the stop codon and an Xba1 cloning site.
  • the PCR product is digested with restriction enzymes BamH1 and Xba1, and ligated into PS610 vector DNA (isolated from a dam-minus E. coli ) digested with BamH1 and Xba1. This creates a fusion between Cys1 and GRB2 under the control of a CMV promoter.
  • the resulting plasmid is referred to as PS628.
  • HSPDE4A1-EGFP fusion To construct the HSPDE4A1-EGFP fusion, the ca. 1.95 kb coding region of HSPDE4A1 (GenBank Acc. no. U97584) is amplified using PCR and primers 4A1-top and 4A-boftom described below.
  • the top primer includes specific HSPDE4A1 sequences following the ATG, a Kozak sequence, and a Hind3 cloning site.
  • the bottom primer includes the common PDE4A C-terminal sequence minus the stop codon, a BamH1 cloning site, and two extra nucleotides to preserve the reading frame when inserted into in pEGFP-N1.
  • the PCR product is digested with restriction enzymes Hind3 and BamH1, and cloned into pEGFP-N1 (Clontech, Palo Alto; GenBank Accession number U55762) cut with Hind3 and BamH1.
  • the resulting plasmid is referred to as PS461 and is deposited under the Budapest Treaty with Deutsche Sammiung von Mikroorganismen und Zellkulturen GmbH (DSMZ) on Apr. 17, 2000 with DSM 13449.
  • This example describes protocols and methods used for in vivo expression of the probes described in Example 1, and the visualisation and measurement of changes undergone by EGFP fusion probes, either transfected singly or as co-transfections with anchor probes in CHO cells.
  • CHO Chinese hamster ovary cells
  • Stable transfectants of single GFP probes are selected using the appropriate selection agent, usually 0.5 mg/ml G418 sulphate (Calbiochem) in the growth medium (HAM's F12 nutrient mix with Glutamax-1, 10% foetal bovine serum (FBS), 100 ⁇ g penicillin-streptomycin mixture ml ⁇ 1 (GibcoBRL, supplied by Life Technologies, Denmark).
  • the appropriate selection agent usually 0.5 mg/ml G418 sulphate (Calbiochem) in the growth medium (HAM's F12 nutrient mix with Glutamax-1, 10% foetal bovine serum (FBS), 100 ⁇ g penicillin-streptomycin mixture ml ⁇ 1 (GibcoBRL, supplied by Life Technologies, Denmark).
  • Co-transfected cells are cultured in the same medium but with the addition of a two selection agents appropriate to the plasmids being used, usually 0.5 mg/ml G418 sulphate plus 1 mg/ml zeocin. Cell are cultured at 37° C. in 100% humidity and conditions of norrnal atmospheric gases supplemented with 5% CO 2 .
  • Clonal cell lines with particular properties are sub cultured from mixed populations of stably transfected cells by isolating individual cells and removing them to sterile culture flasks containing fresh culture medium with 0.5 mg/ml G418 sulphate or 0.5 mg/ml G418 sulphate+1 mg/ml zeocin as appropriate to the plasmid(s) being selected.
  • cells are allowed to adhere to Lab-Tek chambered coverglasses (Nalge Nunc International, Naperville USA) for at least 24 hours and are then cultured to about 80% confluence. Cells can also be grown in plastic 96-well plates (Polyfiltronics Packard 96-View Plate or Costar Black Plate, clear bottom; both types tissue culture treated) for imaging purposes. Prior to experiments, the cells are cultured over night without selection agent(s) in HAM F-12 medium with glutamax, 100 ⁇ g penicillin-streptomycin mixture ml ⁇ 1 and 10% FBS. This medium has low autofluorescence enabling fluorescence microscopy of cells straight from the incubator.
  • the HAM's culture medium is replaced prior to imaging with a buffered saline solution (KRW buffer) containing (in mM) 3.6 KCl, 140 NaCl, 2 NaHCO 3 , 0.5 NaH 2 PO 4 , 0.5 MgSO 4 , 1.5 CaCl 2 , 10 Hepes, 5 glucose, pH7.4.
  • KRW buffer buffered saline solution
  • Confocal images are collected using a Zeiss LSM 410 microscope (Carl Zeiss, Jena, Germany) equipped with an argon ion laser emitting excitation light at 488 nm. In the light path are a FT510 dichroic beamsplitter and a 515 nm long-pass filter or a 510 to 525 nm bandpass emission filter. Images are typically collected with a Fluar 40X, NA: 1.3 oil immersion objective, the microscope's confocal aperture set to a value of 10 units (optimum for this lens).
  • Image sequences of live cells over time are gathered using a Zeiss Axiovert 135M fluorescence microscope fitted with a Fluar 40 ⁇ , NA: 1.3 oil immersion objective and coupled to a Photometrics CH250 charged coupled device (CCD) camera (Photometrics, Arlington, Ariz. U.S.A.).
  • the cells are illuminated with a 100 W HBO arc lamp.
  • In the light path are a 470 ⁇ 90 nm excitation filter, a 510 nm dichroic mirror and a 515 ⁇ 15 nm emission filter for minimal image background.
  • the cells are maintained at 37° C. with a custom-built stage heater.
  • Time lapse response profiles are extracted from image sequences using a region of interest (ROI) defined over the same co-ordinates or pixels for each successive image in a sequence: pixel values are summed and averaged over the ROI in each image, and the resulting values plotted against image number to generate a time lapse response profile for that defined region of the sequence.
  • ROI can include many cells, a single cell, or a region within a single cell.
  • the amount of fluorescent spots and other accumulations of a transfected probe in a population of cells can be imaged and quantified in an automated fashion to yield a measure of mean number of spots per cell.
  • cells are cultured to near 80% to 90% confluence in coverglass chambers or plastic 96-well plates, given the relevant treatment and allowed to respond.
  • cells are chemically fixed in 4% formaldehyde buffer (Lillies fixative buffer, pH7.4: Bie and Berntsen A/S, Denmark) for 30 minutes to 2 hours, and then washed three times in phosphate buffered saline (PBS, Life Technologies, Denmark).
  • An alternative simultaneous fixation+permeabilisation method useful to remove non-localised (i.e.
  • GFP probe from the cytoplasm involves a single fixation process incorporating 0.4% to 2% formaldehyde buffer (10% to 50% strength Lillies fixative) plus 0.2% to 1% Triton X-100.
  • the actual concentrations used need to be optimised for the cell type being used; for CHO cells 2% formaldehyde+1% Triton X-100 gives excellent results.
  • the combined fixative+detergent are applied to the cells for 10 to 20 minutes at room temperature. Cells are then washed three times with phosphate buffered saline.
  • Nuclear DNA is stained with 10 ⁇ M Hoechst 33258 (Molecular Probes, Eugene, Oreg., U.S.A.) in PBS for 10 minutes at 25° C., then washed twice in PBS. Automated images are collected on a Nikon Diaphot 300(Nikon, Japan) using a Nikon Plan Fluor 20X/0.5NA objective lens. The basic microscope is fifted with a motorised specimen stage and motorised focus control (Prior Scientific, Fulbourn, Cambridge UK), excitation filter wheel (Sutter Instruments, Novato Calif. U.S.A.) and Photometrics PXL series camera with a KAF1400 CCD chip (Photometrics, Arlington, Ariz.
  • Both images are collected via the same dichroic and emission filters, which are optimised for EGFP applications (XF100 filter set, Omega Optical, Brattleboro, Vt.). While the choice of filters for imaging the nuclear stain (Hoechst 33258) is not well matched to that dye's spectral properties, resulting in lower image intensity, it greatly improves the throughput of the procedure by allowing both images to be collected using the same dichroic and emission filter. This eliminates any image registration problems and focus shifts which would result from using two different filter sets, which would require more steps in the acquisition procedure and more extensive image processing to overcome.
  • the necessary images are collected as follows: A holder containing four 8-well coverglass chambers, or a single 96-well plate, is loaded onto the microscope.
  • the program is started, and the first well of cells is moved into position and manually coarse-focused by the operator.
  • the image is fine-focused by an auto-focus routine using the 340/10 excitation.
  • An image is captured and stored at this excitation wavelength (the nuclear image), and then a second image is captured and stored at the longer wavelength excitation (the GFP image).
  • the stage is automatically repositioned and microscope automatically refocused to capture a second pair of images within the same well. This process is repeated a set number of times (typically 4 to 8) for the first well.
  • the stage then advances the next well to the imaging position, and the process repeats itself until the set number of image pairs has been captured from each well of cells.
  • Image pairs are automatically analysed in the following way using a suite of macros running under the IPLab Spectrum software: First the nuclear image of a pair is filtered with a digital filter to simultaneously sharpen the edges of and suppress differences in intensity of the nuclei. The choice of filter, and the filter constants, were arrived at through experimentation with various data sets. The filtered image is then segmented at a pre-determined intensity value, such that pixels below this threshold are very likely not within a nuclear region, and pixels above this threshold are very likely within a nuclear region.
  • the contiguous regions above the threshold are then counted, after rejecting contiguous regions that are larger than a certain area or smaller than a certain (different) area, the areas having been previously determined to provide a sufficiently accurate distinction between nuclei and other objects that are not nuclei.
  • the final count is the estimated number of nuclei in the field.
  • the GFP image of each pair is then digitally filtered with a filter chosen experimentally to suppress the variation of intensity due to the typical non-localised distribution of GFP, while accentuating the intensity of any bright point-like objects relative to this background.
  • This filtered image is then segmented at a threshold that has been experimentally determined to divide the image into pixels that are very likely to be in a spot (above the threshold) and pixels that are very likely not to be in a spot (below the threshold).
  • the contiguous regions of pixels that are above the threshold are counted, after rejecting regions that do not have certain morphological properties, which were previously determined to be characteristic of spots.
  • the ratio of spot count to nuclear count for each pair represents an estimate of the average number of spots per cell in that image pair. All image pairs are treated in this way, and the final table of values is used to establish the cellular response to a given treatment.
  • FIG. 3 is an example of how the effect of a compound upon spot density in CHO cells expressing HSPDE4A4-EGFP can be measured using the automated imaging and image analysis method.
  • the amount of fluorescent spots and other accumulations of a transfected probe in a population of cells can also be quantified using a fluorescent plate reader, such as a TECAN Spectrafluor (Tecan U.S. Inc., Research Triangle Park, N.C. 27709, U.S.A.) or using a fluorescence imaging plate reader (FLIPR; Molecular Devices Corp., Sunnyvale, Calif. 94089, U.S.A.).
  • FLIPR fluorescence imaging plate reader
  • FIG. 4 is an example of the use of the FLIPR to measure the effect of a compound upon spot density in CHO cells expressing HSPDE4A4-EGFP. The cells were treated with the simultaneous fix and permeabilisation protocol to obtain these data.
  • Redistributions of fluorescent probes from cytoplasm to plasma membrane may be quantified by standard imaging methods using simple image analysis of the changes in fluorescence intensity of cytoplasmic ROls. Similar redistributions may also be measured on the FLIPR, and even on standard fluorescent plate readers, especially those configured to measure signal from adherent cells in microtitre plates.
  • FIG. 7 shows how the effect of a compound on the redistribution of Cys1 ⁇ -EGFP can be quantified using the FLIPR.
  • Example 4 and Example 6 describe generic ways to produce a cell line suitable for screening compounds targeting against a specific interaction between two partner components X and Y.
  • the cells are derived from CHO cells co-transfected with two plasmids, one coding for fusion probes with X or Y attached to either the C or N terminal of the anchor moiety (the anchor probe), and the second with the other partner, Y or X, attached to either the C or N terminal of GFP (the detectable probe).
  • the anchor probe the anchor probe
  • the detectable probe attached to either the C or N terminal of GFP
  • Anchor and detectable probes use different selection markers to ensure that cells under selection maintain both plasmids; for example, the anchor may confer resistance to zeocin, the detectable to neomycin. Cells that maintain both probes under continuous selection (minimum of 2 weeks) are termed “stable”.
  • the anchor probes are based on HSPDE4A4B (human phosphodiesterase type 4, isoform A, splice variant 4B: referred to hereafter as PDE4A4), which when treated with the PDE4 inhibitor rolipram forms a number of dense aggregates in the cytoplasm of each cell (EC 50 0.2 to 0.3 ⁇ M). These rolipram-induced aggregates may be detected with an antibody directed against the unique C-terminal peptide sequence of HSPDE4A, as demonstrated in FIG. 10 .
  • HSPDE4A4B human phosphodiesterase type 4, isoform A, splice variant 4B: referred to hereafter as PDE4A4B
  • PDE4A4B human phosphodiesterase type 4, isoform A, splice variant 4B
  • Test for conditional association with an appropriate interaction stimulus A and B can be done in parallel. B tests for possible conditions or associations that can only occur in the “soluble phase”.
  • the anchor probes are based on HSPKAcat ⁇ (catalytic subunit of human cyclic AMP-dependant protein kinase, isoform ⁇ : hereafter referred to as PKAc), which when transfected into cells forms aggregates in the cytoplasm under conditions of low cytoplasmic cAMP concentrations. These aggregates may be detected with an antibody directed against PKAc, also with antibodies directed against the PKA regulatory subunit type 1 ⁇ (R1 ⁇ ). In cells successfully transfected with a plasmid coding for a fusion protein having GFP fused to the C-terminal of PKAc, such aggregates are seen as bright green fluorescent spots in the cell ( FIG. 5 ).
  • Test for conditional association with an appropriate interaction stimulus A and B can be done in parallel. B tests for possible conditions or associations that can only occur in the “soluble phase”.
  • the anchor probes are based on PDE4A1 domains.
  • PDE4A1 accumulates as small perinuclear spots in otherwise untreated cells. These spots are readily detected wioth an antibody raised against the unique C-terminal portion of PDE4A. Treatment with rolipram causes these spots to disperse into the cytoplasm ( FIG. 13 ). Subsequent removal of rolipram results in the rapid re-appearance of perinuclear spots.
  • FIG. 13 a CHO cells stably expressing HSPDE4A1-GFP are growing in only HAM's F12 medium with 10% FBS; the GFP fluorescence is restricted to bright granule-like spots within the perinuclear cytoplasm of each cell. The spots may be clustered around, in or on the Golgi membranes.
  • FIG. 13 b similar cells to those seen in 13 a have been treated with 2 micromolar rolipram for 2 hours. The majority of GFP-bright spots disappear in all cells under rolipram treatment, and the cytoplasm becomes generally brighter. Larger spots may not disperse completely in some cells. When rolipram is washed away, the spots reform within 1.75 hours.
  • FIG. 14 shows a dose response curve for spot dispersal in response to rolipram.
  • the number of spots per cell for each concentration of rolipram is the mean of 4 measurements ⁇ sem, where each measurement is itself an average taken from not less than 100 cells.
  • Cells are grown in HAM's F12 medium plus 10% FBS plus various concentrations of rolipram for 7 hours. The cells are then chemically fixed with 4% formalin buffer (pH7.5) for 15 minutes, washed with PBS and stained with 10 PM Hoechst 33258 in PBS for 10 minutes at 25° C., then washed twice in PBS. Automated images are collected and analysed for the number of spots per cell as described in Example 2.
  • Test for conditional association with an appropriate interaction stimulus A and B can be done in parallel. B tests for possible conditions or associations that can only occur in the “soluble phase”.
  • the anchor probes are based on the Cys1 domain of PKC ⁇ (Cys1 domain of protein kinase C isoform ⁇ ) in which coding sequences for the myc or flag antigens are optionally included, which when transfected into cells has a general cytoplasmic distribution that redistributes to the plasma membrane when treated with PMA (phorbol-12-myristate-13-acetate).
  • PMA phorbol-12-myristate-13-acetate
  • the redistribution from cytoplasm to plasma membrane may be detected with an antibody directed against the Cys1 domain of PKC ⁇ , or with antibodies directed against the myc or flag antigens, if these have been engineered into the Cys1 construct.
  • Test for conditional association with an appropriate interaction stimulus A and B can be done in parallel. B tests for possible conditions or associations that can only occur in the “soluble phase”, before targeting to PM is imposed.
  • This example demonstrates the use of the redistribution trap method to create a cell line suitable for screening compounds against the interaction between Sos and Grb2, components involved in the signalling pathway immediately downstream from certain tyrosine kinase receptors located at the plasma membrane of mammalian cells, for example the insulin and the epidermal growth factor receptors.
  • Sos is a guanine nucleotide exchange factor responsible for activation Ras-like GTPases
  • Grb2 an adaptor component responsible for recuiting Sos to the activated receptor.
  • the anchor probe is based on HSPDE4A4.
  • FIG. 8 a is a confocal image of such cells growing in HAM's F12 medium with 10% FBS and FIG. 8 b shows similar cells after treatment with 10 ⁇ M rolipram.
  • the transfected cells are a mixed non-clonal population.
  • the GFP-labelled detectable probe (GFP fluorescence) is distributed throughout the cell prior to rolipram treatment, with a slightly higher concentration in the nuclei.
  • FIG. 8 b After rolipram treatment (20 hours) some cells, in clonal groups, develop distinct bright spots ( FIG. 8 b ). The appearance of the spots, and the requirement for rolipram, indicate that in these cells the anchor probe has responded to rolipram as PDE4A4 is expected to ( FIG. 2 ), and that the GFP-labelled detectable probe must be associated with it.
  • the PDE4 specific inhibitor RP73401 is applied in the presence of rolipram ( FIG. 9 ). RP73401 competes with rolipram and causes PDE4A4 spots to disperse ( FIG. 3 and 4 ). As can be seen in FIG.
  • the spots disappear with RP73401 treatment, confirming that it is the anchor probe that is responsible for the spotty distribution of the detectable probe, and thus that anchor and detectable pairs are interacting.
  • HSPDE4A4 and EGFP do not interact when co-transfected and rolipram treated (not shown, but EGFP distribution is always pan-cellular, in both nucleus and cytoplasm in such cells, and its distribution is unaffected by rolipram), the interaction must be mediated by the natural interaction of Sos and Grb2.
  • the co-transfected cells When cloned, the co-transfected cells may be used for screening compounds against the Sos-Grb2 interaction.
  • This example describes the creation of a cell line suitable for screening compounds against the interaction between Grb2 and the C-terminal sequence of Sos (amino acids 1067 to 1332 of Sos).
  • This is similar to the interaction pair described in Example 7, except that the anchor probe is based upon the catalytic subunit of cAMP-dependent protein kinase isoform ⁇ (HSPKAcat-hGrb2), and therefore locates in unstimulated cells as aggregates, which if they attract the detectable probe (EGFP-Sos-Cterm) will become GFP-bright.
  • HPKAcat-hGrb2 catalytic subunit of cAMP-dependent protein kinase isoform ⁇
  • EGFP-Sos-Cterm detectable probe
  • CHO cells are stably co-transfected with the anchor probe HSPKAcat-hGrb2 and GFP-labelled detectable probe EGFP-Sos-Cterm as described in Example 2 and Example 4.
  • the anchor probe is selected for with zeocin, and the detectable probe with neomycin (G418).
  • CHO cells stably expressing both the anchor probe HSPKAcat-hGrb2 and GFP-labelled detectable probe EGFP-Sos-Cterm are shown in FIG. 11 before ( FIG. 11 a ) and 10 minutes after ( FIG. 11 b ) treatment with 50 micromolar forskolin+500 micromolar IBMX. Three cells are evident in ( FIG.
  • This example describes the creation of another cell line suitable for screening compounds against the interaction between Grb2 and the C-terminal sequence of Sos (amino acids 1067 to 1332 of Sos).
  • This is the same interaction pair described in Example 6, except that the anchor probe is based upon the Cys1 domain of protein kinase C isoform gamma, and therefore locates in unstimulated cells throughout the cytoplasm and nucleus.
  • the anchor probe redistributes to the plasma membrane, and if an interaction occurs between anchor and detectable probes, the GFP fluorescence will also be seen to redistribute to the plasma membrane.
  • an advantage of this anchor system is that when stimulated with PMA, the anchor probe is taken to the plasma membrane where it will come into close proximity with other components that may be important in modulating the interaction between the components attached to the anchor and EGFP moieties.
  • Grb2 and Sos-Cterm proximity to the plasma membrane does not appear to be necessary in order to initiate their interaction, but certain component pairs may fail to interact unless this condition is met.
  • Treatment with PMA is used to confirm that an interaction between anchor and detectable probes occurs in this system, since redistribution of fluorescence to the plasma membrane can only occur if interaction of the two probes has first taken place. This can be checked in CHO cells transfected with EGFP-Sos-Cterm alone, where PMA has no effect on the distribution of fluorescence.
  • FIG. 12 shows CHO cells stably expressing both the anchor probe Cys1-hGrb2 and GFP-labelled detectable probe EGFP-Sos-Cterm before ( FIG. 12 a ) and 5 minutes after ( FIG. 12 b ) treatment with 100 nM PMA.
  • the majority of cells in before PMA treatment have a rather general cytoplasmic and nuclear distribution of fluorescence.
  • the selective PDE4 inhibitor rolipram affects the physical properties and behaviour of PDE4A4 such that the general cytoplasmic distribution of PDE4A4 in most cells gradually changes to one consisting of concentrations of PDE4A4 located at several distinct spots within the cytoplasm (see Example 3).
  • This example illustrates how binding between the 14-3-3 protein and BAD can be visualized using the PDE4A4-14-3-3beta and eGFP-BAD fusions. It is an example of a change in mobility from a soluble cytoplasmic state to a state wherein the eGFP-BAD fusion is attached, or actually aggregated in the cytoplasm.
  • Cell type CHO cells transfected with one plasmid expressing an in frame protein fusion between PDE4A4 and human 14-3-3beta and another plasmid expressing an in frame protein fusion between EGFP and human BAD (details on the construction of such probes can be found in examples 1 and 3).
  • Density 1.0 ⁇ 10E5/well (the day they are seeded), in 96-well microtitre plates (ViewPlate-96, Black; Packard)
  • Cells are plated in 1.0 ⁇ 10E5/well in 200 ⁇ l HAM F-12 w. 10% FCS and 5% pen/strep 20-24 hrs before screening. Stimulated cells are further added 10 ⁇ M rolipram.
  • test compound is added on top of the 200 ⁇ l HAM F-12 growth medium and incubated for 2 hrs in CO 2 incubator HAM F-12 with test compound is drained from all wells of the microtitre plate and cells are extracted in 200 ⁇ l extraction buffer for 5 min.
  • Cells are added 100 ⁇ l formaldehyde 4% buffer on top of the 200 ⁇ l extraction buffer and are incubate for 5 min.
  • Extraction buffer is drained and cells are washed ⁇ 2 in 100 ⁇ l PBS. Cells are added 200 ⁇ l PBS buffer.
  • the fluorescence is read in ASCENT plate reader using a pre-programmed procedure and filter settings suitable for GFP and Hoechst 33258 fluorophores.
  • the Hoechst reading is used to provide a signal by which cell number can be estimated, and thereby useful in normalising GFP signals from wells that may not contain identical number of cells.
  • the results are presented in FIG. 15 .
  • NFkB(p65) moves from cytosol to nucleus upon stimulation of NFkB with II-1. This can be visualized with a NFkB(p65)-GFP fusion.
  • the total GFP intensity measured after removing cytosolic NFkB(p65)-YGFP is indicative of the degree of translocation to the nucleus, and thus of the degree of activation of NFkB. This is an example of a change in mobility as a change from a soluble cytoplasmic NFkB to a component attached in the nucleus.
  • the difference between non-stimulated and stimulated cells can be read by the intensity of fluorescence (see FIG. 16 ).
  • Stimulated and non-stimulated cells are extracted with different combinations of triton-x 100 and formalin and the signal is read in a plate reader.
  • the aim is to identify the ratio between formalin and triton-x that gives the optimal signal to noise (s/n) ratio.
  • the s/n is calculated as (fluorescence in stimulated cells minus the fluorescence in non-stimulated cells) divided by the fluorescence in the non-stimulated cells times 100%.
  • s / n ( stimulated ⁇ ⁇ cell - non ⁇ ⁇ stimulated ⁇ ⁇ cells ) non ⁇ ⁇ stimulated ⁇ ⁇ cells * 100 ⁇ ⁇ %
  • the optimization is illustrated in FIG. 17 .
  • PKAcat-GFP forms distinct spots in its inactive tetrameric form.
  • PKAcat Upon increase in cellular cAMP (e.g. by stimulation of adenylate cyclase activity by forskolin) PKAcat dissociates from its regulatory subunits and spots “dissolves” into the cytosol.
  • the total GFP intensity measured after removing cytosolic PKAcat-GFP through the extraction procedure is indicative of the level of non-activated, non-dissociated PKAcat.
  • the extraction procedure is used to quantify a forskolin dose response in a PKAcat-GFP assay.
  • the PDE4 inhibitor rolipram is used to stimulate the production of the dense aggregates 5 of PDE4A4 in the cytoplasm of cells transfected with fusions to PDE4A4 described in Example 3.
  • a possible concern of using such a stimulus is that levels of the second messenger molecule cAMP, the substrate for PDE4 enzymes, may increase in rolipram treated cells to such an extent that unwanted cAMP-dependent processes in those cells may also become activated.
  • cAMP-dependent effector proteins include the PKA family of kinases, some ion channels and certain guanine nucleotide exchange factors such as cAMP-GEF1 and 2.
  • CHO cells stably expressing HSPDE4A4B-GFP (see Example 2), and untransfected CHO cells are seeded into individual wells of a 96-well microtiter plate at a density of 1.2 ⁇ 10 5 cells/well, and cultured for 16 to 18 hours in HAM F-12 medium with glutamax, 100 ⁇ g penicillin-streptomycin mixture ml ⁇ 1 and 10% FBS plus various concentrations of rolipram. After the incubation period, cAMP content is measured using a commercial kit from Amersham-Pharmacia Biotech, kit # RPA538, according to the manufacturers instructions.
  • the amount of cAMP/well was calculated using regression analysis from a cAMP standrad curve, as recommended by the manufacturers of the assay kit. The results of this experiment are shown in FIG. 19 .
  • the curves for both normal untransfected CHO cells ( ⁇ ), and cells stably expressing HSPDE4A4B-GFP ( ⁇ ) show no appreciable increase in cellular cAMP concentration over a range of rolipram treatments from 0.03 ⁇ M to 3 ⁇ M.
  • the slight rise in cAMP in normal CHO cells at 10 ⁇ M rolipram is probably not significant, since this concentration is between 30 to 300 fold higher than any reported IC 50 value for inhibition of any known isoform of PDE4 by rolipram.
  • HSPDE4A4-GFP fusion protein is an active phosphodiesterase enzyme and that its greatly increased expression effectively prevents any cAMP increase in these cells despite adenylate cyclase activation by forskolin over the range tested.
  • FIG. 1 A first figure.
  • RP73401 Dose response of RP73401 versus 3 ⁇ M rolipram in clonal cells expressing HSPDE4A4-EGFP.
  • Cells have been seeded into a 96-well Packard ViewPlate and grown in HAM's F12 medium plus 10% FBS plus 3 ⁇ M rolipram to approximately 80% confluence.
  • rolipram treatment was for a total of 16 hours.
  • Various concentrations of RP73401 were added to the rolipram-containing wells and incubated for a further 4 hours. The cell were then chemically fixed, washed and stained with Hoechst 33258, and a measurement of mean spots per cell made for each treatment well using an automated imager, all as described in Example 2.
  • Results have been fitted to a 4-parameter Hill plot, and yield an IC 50 figure of approximately 50 nM for the competitive inhibition by RP73401 of spot formation by 1 ⁇ M rolipram.
  • Successive images show how the fluorescently tagged catalytic subunit of PKA redistributes from the bright aggregates into the cytoplasm over a period of minutes as cAMP levels increase in the cells as a result of forskolin treatment.
  • Scale bar 10 microns.
  • Cells are a clonal cell line growing in HAM's F12 medium plus 10% FBS. After 5 minutes treatment with 100 nM PMA (b), the fluorescently tagged Cys1 domain of PKCgamma redistributes from the cytoplasm and nucleus to the plasma membrane.
  • a clonal CHO cell line stably expressing the Cys1 domain of the human isoform of PKC gamma tagged with GFP in its C-terminal end was cultured in 96-well microliter plates (Packard View-Plate). After 20 min preincubation in KRW (experimental buffer; A modified Krebs-Ringer buffer containing (in mM): NaCl 140, KCl 3.6, NaH2PO4 0.5, MgSO4 0.5, NaHCO3 2.0, CaCl2 1.5 and HEPES 10, D-glucose 5 (pH 7.4, btrated with 1M NaOH)) the cell plate was placed in the FLIPR.
  • KRW experimental buffer; A modified Krebs-Ringer buffer containing (in mM): NaCl 140, KCl 3.6, NaH2PO4 0.5, MgSO4 0.5, NaHCO3 2.0, CaCl2 1.5 and HEPES 10, D-glucose 5 (pH 7.4, b
  • the cells were stimulated in place on the FLIPR machine with the phorbol ester PMA given in doses from 10 ⁇ M to 0.5 nM in 1:3 steps.
  • CHO cells expressing HSPDE4A4-EGFP have been treated with 10 ⁇ M rolipram for 20 hours then chemically fixed and immunostained with an antibody raised in an ovine host against a peptide identical to a portion of the unique C-terminal sequence of HSPDE4A enzymes.
  • the antibody is detected using Alexa 549-conjugated donkey anti-sheep antibody (Molecular Probes Inc., Oregon, USA). This pair of confocal micrographs show the image of EGFP fluorescence in the cells (a) in comparison to that obtained for Alexa 549 fluorescence (b). Emission filters (a: 515-525 nm bandpass.
  • FIG. 14 shows a dose response curve for PDE4A1 spot dispersal in response to rolipram.
  • the number of spots per cell for each concentration of the different inhibitors is the mean of 4 measurements ⁇ sem, where each measurement is itself an average taken from not less than 100 cells.
  • Cells are grown in HAM's F12 medium plus 10% FBS plus various concentrations of rolipram for 7 hours. The cells are then chemically fixed with 4% formalin buffer (pH7) for 15 minutes, washed with PBS and stained with 10 ⁇ M Hoechst 33258 in PBS for 10 minutes at 25° C., then washed twice in PBS. Automated images are collected and analysed for the number of spots per cell as described in Example 2.
  • CHO cells stably expressing HSPDE4A4B-GFP (see Example 2), and untransfected CHO cells are seeded into individual wells of a 96-well microtiter plate at a density of 1.2 ⁇ 10 5 cells/well, and cultured for 16 to 18 hours in HAM F-12 medium with glutamax, 100 ⁇ g penicillin-streptomycin mixture ml ⁇ 1 and 10% FBS plus various concentrations of rolipram. After the incubation period, cAMP content is measured using a commercial kit from Amersham-Pharnacia Biotech, kit # RPA538, according to the manufacturers instructions.
  • the amount of cAMP/well was calculated using regression analysis from a CAMP standrad curve, as recommended by the manufacturers of the assay kit.
  • the curves for both normal untransfected CHO cells ( ⁇ ), and cells stably expressing HSPDE4A4B-GFP ( ⁇ ) show no appreciable increase in cellular cAMP concentration over a range of rolipram treatments from 0.03 ⁇ M to 3 ⁇ M.
  • the slight rise in cAMP in normal CHO cells at 10 ⁇ M rolipram is probably not significant.
  • CHO cells stably expressing HSPDE4A4B-GFP (see Example 2), and untransfected CHO cells are seeded into individual wells of a 96-well microtiter plate at a density of 1.2 ⁇ 10 5 cells/well, and cultured for 16 to 18 hours in HAM F-12 medium with glutamax, 100 ⁇ g penicillin-streptomycin mixture ml ⁇ 1 and 10% FBS. After 16 to 18 hours incubation, cells are treated for 60 minutes with various concentrations of forskolin. After the treatment period, cAMP content is measured using a commercial kit from Amersham-Pharmacia Biotech, kit # RPA538, according to the manufacturers instructions.
  • the amount of cAMP/well was calculated using regression analysis from a cAMP standrad curve, as recommended by the manufacturers of the assay kit.
  • the curve for normal untransfected CHO cells ( ⁇ ) shows the expected dose-dependent increase of cellular cAMP in response to this adenylate cyclase activator.
  • Cells stably expressing HSPDE4A4B-GFP ( ⁇ ) show no appreciable increase in cellular CAMP concentration over a range of forskolin treatments from 0.3 ⁇ M to 100 ⁇ M.

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